Infection of Nomuraea riley CQNr01 against Larvae of Spodoptera litura

Virulence of Nomuraea riley CQNr01 against the 2nd and 4th instar larvae of Spodoptera litura was investigated.Spore germination and appressorium formation on isolated epidermis of S.litura was observed by fluorescence microscopy.Results indicated at the concentration of 1×108 and 1×109 spores·mL 1,the mortality of the 2nd instar larvae caused by N.riley CQNr01 was 86.58% and 89.91%,respectively,while the mortality of the 4th instar larvae was only 13.33% and 16.67%.Under fluorescence microscopy,spores of CQNr01 were found adhered to isolated epidermis of the 2nd and the 4th instar larvae,and spores germinated within 24 h post inoculation,while adhesion strength of the 2nd instar larvae was stronger.The germ tubes grew longer and the germination rate became larger as the inoculation time went on.However,under the same inoculation time,the germination rate and the number of appressorium on the 2nd instar larvae significantly exceeded to those on the 4th instar larvae.The study showed that virulence of N.riley CQNr01 against the 2nd and the 4th instar larvae was significantly different and the epidermis may be the main reason.